Abbreviation for Noise Reduction Coefficient. This is a specification often used to indicate the effectiveness of acoustic absorption materials. Generally it is arrived at by averaging the Sabine absorption coefficients of a material in the octave bands between 125 Hz to 4 kHz. The higher the number, the more sound is absorbed. The NRC is thus a sort of general result when compared to the detailed information that can be gleaned from good absorption coefficient data across different frequencies. For example, many common household materials such as curtains or carpet are very effective absorbers at 4 kHz, but don’t do much at all to lower frequencies. NRC values don’t include this detail.